Age repair policies for the machine repair problem

Most existing studies of the machine repair problem make the restrictive assumption that repairs are made only after machine failure, i.e. preventive maintenance is ignored. Our work extends this model by incorporating preventive repair for ageing machines. We derive a maintenance policy with a single critical age, determine its properties, and suggest the use of service constraints when costs are difficult to estimate. We then introduce the idea of a double critical age policy that uses a wear-out age to improve performance; in our small numerical study the cost savings from use of this policy exceeded 20% in several cases.